1. Field of the Invention
The present invention relates to a connection structure for a battery unit for providing connections between terminals of a plurality of cells.
2. Description of Related Art
In order to improve long-term durability of a battery unit wherein a plurality of cells are connected, it is essential both to improve the characteristics of the elements for electromotive force in the cells and to improve the durability of the connecting sections providing electrical connections between the cells. Specifically, any deterioration due to corrosion of the connecting sections which come into contact with external air will lead to increased electrical resistance, and hence this becomes a major cause of decline in the output characteristics of a battery unit. Therefore, in the prior art, connection structures for preventing corrosion of the connecting sections by sealing them from the external air have been proposed, as disclosed in Japanese Patent Laid-open No.(Hei)10-64507, for example.
Below, a connection structure for a battery according to the prior art is described with reference to FIG. 6-FIG. 8. As shown in FIG. 6, a cell 1 is constituted by elements for electromotive force 3, wherein positive electrode plates and negative electrode plates are layered together, separators being interposed therebetween, which are accommodated and sealed inside a battery case 2 of rectangular cross-section made from synthetic resin, together with an electrolyte. Terminals 5, 6 for the positive electrode and negative electrode are provided respectively projecting from either end portion of the upper face 4 of the battery case 2, these being connected respectively to the positive electrode plates and negative electrode plates via lead plates 7. The terminals 5, 6 penetrate into the interior of the battery case 2 by means of terminal holes formed in the upper face 4 of the battery case 2, and they are fastened by means of fixing washers 8 in a state where a seal is provided between same and the upper face 4 of the battery case 2. Numeral 9 denotes a safety vent for discharging gas in cases where the pressure inside the cell increases abnormally.
As illustrated in FIG. 7, a battery unit 10 is constituted by arranging cells 1 of the aforementioned construction in a parallel configuration, in such a manner that the positive electrode terminals 5 and negative electrode terminals 6 thereof are situated adjacently to each other in an alternating fashion, these adjacent positive electrode terminals 5 and negative electrode terminals 6 being connected by means of connecting members 11.
As shown in FIG. 8, the connecting members 11 are each constituted by a coupling plate 12 made from copper plate for connecting the terminals 5, 6 together, and a cover member 13 made from chloroprene rubber for covering the periphery of the terminals 5, 6 and the coupling plate 12 in such a manner that they are sealed from the external atmosphere.
The coupling plates 12 are respectively made from an oval-shaped plate having connecting holes 12a through which screw shaft portions of the terminals 5, 6 are passed, which is positioned on top of step sections in the base portions of the terminals 5, 6 and fastened by means of nuts 14 screwing onto the screw shaft portions of the terminals 5, 6.
Each cover member 13 comprises tubular sections 15 respectively surrounding the periphery of a terminal 5, 6 and a nut 14, and a coupling section 16 for coupling the tubular sections 15, a coupling plate 12 being embedded integrally inside the cover member 13. Naturally, the coupling plate 12 is exposed inside the tubular sections 15. When coupling plates 12 are fastened tightly onto the terminals 5, 6, the lower end portions of the tubular sections 15 exert pressure on the upper face 4 of the battery case, about the periphery of the terminals 5, 6 via the coupling plate 12. The upper opening portions of the tubular sections 15 are sealed openably by way of lid members 17, in such a manner that they can be closed tightly after the nuts 14 have been fastened.
However, in the connection structure for a battery described above, an external seal is formed by means of the lower ends of the tubular sections 15 pressing against the coupling plates 12, thereby exerting pressure on the upper face 4 of the battery case. Consequently, whilst it is possible to prevent corrosion of the terminals 5, 6 and coupling plates 12 through exposure to the external atmosphere, the tubular sections 15 are liable to deform in an outward radial direction, due to the aforementioned pressure. As a result of this deformation, the seal between the tubular section 15 and the upper face 4 of the battery case becomes insufficient, and consequently, in an operating environment where the battery is exposed to severe variations in temperature conditions, electrolyte seeping between the base portions of the terminals 5, 6 and the fixing washers 8, and between the fixing washers 8 and the upper face 4 of the battery case, as indicated by the arrows in FIG. 8, will flow out at any points where the seal between the lower ends of the tubular sections 15 and the upper face 4 of the battery case is incomplete.